Conventional open-to-atmosphere mud returns systems present a challenge when attempting to obtain energy resources that have previously been deemed economically or technically impossible to drill due to narrow drilling windows. A narrow drilling window significantly reduces the possibility of drilling to targeted depth effectively and efficiently from cost and safety perspectives. However, it is not always the pore pressure and fracture pressure gradients that define the drilling window, as has been observed in a field in East[MA(1] Java Province, Indonesia. In this instance, the actual drilling window lay between the wellbore instability and mud losses pressure gradients. Having the bottom hole pressure lower than the wellbore instability pressure would risk collapse of the wellbore, resulting in stuck pipe, or worse, a fishing job and requirement to sidetrack the well. Thus, a steady bottom hole pressure within that window was deemed critical to successfully drill to the section target depth. The application of Managed Pressure Drilling (MPD) was selected to drill the narrow drilling window and has resulted in being able to successfully drill to the targeted depth without wellbore collapse. Data acquired from system-recorded drilling parameters enabled analysis of the wellbore condition and adjustment of parameters leading to a successful operation. Calculated friction pressure, ECD trend line, flow behavior and most importantly surface back pressure were compared as analysis subjects. The utilization of MPD equipment, including Rotating Control Device (RCD) and Automated MPD Choke Manifold, enables surface back pressure to be applied to create the required bottom hole pressure sufficient to maintain wellbore stability within the narrow drilling window. With real-time results being applied on site, as described further in this paper, drilling hazards related to wellbore instability were significantly minimized, if not completely eliminated.
Pressurized Mud Cap Drilling (PMCD) and Early Kick Detection (EKD) are two unconventional drilling techniques that have been used widely individually, mostly in relation to closed and pressurizable systems and to Managed Pressure Drilling (MPD) applications. However, both techniques are seldom used together as an integrated setup. This paper describes a synergized PMCD and EKD setup and field deployment that was used to successfully drill a well in offshore Kalimantan, Indonesia that had a high pressure formation below a zone prone to severe circulation losses. The key components in the setup were a rotating control device (RCD) and a Coriolis mass flow meter. Using an RCD, the drilling system was converted from a conventional open-to-the-atmosphere to a closed-loop system that allows more precise diversion and accurate well flow monitoring, when used in conjunction with a Coriolis mass flow meter. Since it is a closed system, the comparison of the flow coming out of the well with the flow pumped into the well will provide advance information regarding any influx or outflux from the system. The system designed also takes into consideration the efficiency in switching between modes, that is, from conventional drilling to PMCD mode or to EKD mode and then, back to conventional mode. Possible improvements to the system and equipment are also discussed in the paper, as well as how the current system was utilized to successfully drill a well that previously involved multiple sidetracks when attempting to drill conventionally to target depth.
Drilling through narrow window between pore and fracture pressure using Managed Pressure Drilling (MPD) approach requires precise hydraulic designs and pressure control plans to achieve drilling to target depth safely in timely manner which require accurate hydraulic model on pressure changes behavior along the borehole.This paper presents a case study where a non-isothermal hydraulic model was validated using field data from successful Deepwater MPD well in Offshore East Kalimantan, Indonesia. The validation considers all relevant hydraulic parameters such as bottom-hole pressure, equivalent circulating density, circulating friction and surface back pressure. The hydraulic modelling validation results are important in order to determine the non-isothermal hydraulic simulator behavior against actual field data for continuous improvement for future MPD operation.The validation confirmed the previous theoretical estimations that mud density and annular friction considerably depend on dynamic annular temperature profile. The work revealed that using a field-proof non-isothermal hydraulic model plays critical role in order to gather accurate BHP control in MPD operations.During the MPD operations, employing real-time hydraulic model validated by PWD data will improve the dynamic pressure control during the operation, the accuracy, and reliability of the hydraulic simulation results. Hence, enhancing the MPD capability to assist drilling a well to zone of interest more safely and efficient.
Bottomhole pressure management is essential to address challenging issues in hostile drilling environmentsbecause of wellbore pressure disparity during pump cycles while in circulating or noncirculating modes. This disparity can cause substantial instability on equivalent circulating density (ECD). While drilling in deepwater, HPHT, or any other hostile environment, these conditions may result in costly nonproductive time, may jeopardize operational safety, or may disrupt the well drillability. One of the most advanced methods to enhance ECD management during drilling and connection is use of a sub-based uninterrupted circulating system. This technology has been proven to improve drilling performance by maintaining continuous circulation during drilling and connection to retain wellbore pressure stability without significant changes to the rig operation system. This system enables operators to improve drilling performance in wells with a slim pressure window, challenging geomechanical instability, extreme temperature (geothermal), high and long tangent section where hole cleaning is very essential, as well as in extended reach. This system also can be easily integrated with managed pressure drilling technology that exists in the present market. This system uses a small-footprint, sub-based system with an automated flow switching mechanism to eliminate personnel exposure to the high-pressure system. By maintaining steady state circulation throughout the drilling process, the CFS remedies wellbore pressure disparity to retain continuous circulation and ECD management along the entire wellbore. This condition can effectively assist the operator to reduce nonproductive time, to enhance operational safety, and to enable drilling the well to target depth in a timely and safe manner. This paper will describe the equipment design of this uninterrupted circulating system as well as the best practice and constraints during operation. Generic factory testing will also be discussed to provide comprehensive understanding the reliability of the system.
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